[3][4][5] PSDE was formed following a split in the Spanish Social Democratic Union (USDE) of Dionisio Ridruejo.

[12] García López was accused of being a CIA agent, a fact that made other groups suspicious of PSDE.

[17] In early 1976 a group in Valencia broke away from PSDE and formed the Unified Democratic Socialist Party (PSDU).

[22] In November 1976 workers from PSDE and RSE joined the PSOE(H) trade union, Unión General de Trabajadores (sector histórico) (UGT(H)).

[8] In February 1977 PSDE, PSOE(H), RSE and the Social Democratic Federation (FSD) formed a new alliance, the Centre-Left Electoral Union.

FSD had left the Centre-Left Electoral Union, and RSE was expelled from the Democratic Socialist Alliance due to differences with PSOE(H).

[28] In February 1977, the vice presidents Pérez del Campo and Prados Arrarte left the party.

[31][32][33] Towards the end of June 1977 the leaderships of both PSDE and PSOE(H) declared that the Democratic Socialist Alliance had been dissolved.